Exemplary embodiments of the present invention relate to a device for radiometric calibration of infrared image sensors.
Infrared sensors with multi-element detectors must be calibrated before use in order to reduce interference structures—also referred to as fixed-pattern noise—on the sensors to a degree comparable to the temporal noise. To this end, the sensor is directed at a black body with a uniform temperature, the output signal from the detector elements is measured and correction coefficients are determined therefrom, the latter being used to equalize the signals to the same level. By virtue of carrying out this procedure for various black-body temperatures, it is possible to carry out higher order corrections for the temperature. As a result, an IR image is obtained which is free from artifacts over a broad temperature range.
Temperature-stabilized black bodies are commercially available. IR image sensors with a large field of view, e.g., with a fisheye optical unit, can only be calibrated in sections with the aid of such commercially available, planar black-body surfaces. This requires much time and leads to matching problems in the overlap regions.
German Patent Document DE 195 31 536 C2 discloses a device for radiometric calibration of IR measuring devices that uses a metal plate as a black-body surface. The metal plate is provided with a hood in the form of a dome, which is mirrored on the inside and has an opening, serving as aperture, at the vertex. An IR measuring device to be calibrated can be placed into this aperture. This arrangement creates a surface with a luminance that is as uniform as possible. In order to calibrate the whole of an IR image sensor with a large field of view with the aid of this device, the entrance pupil of the sensor must be brought into the aperture of the device. However, since the entrance pupil lies within the optical unit and not in front of the front lens in the case of a wide-angle optical unit, shadowing effects by the image sensor itself cannot be avoided, which can affect the luminance for large angles of view.
It is an object of the invention to develop a device by means of which it is possible to create a uniform luminance that is independent of the viewing angle in order also to calibrate IR image sensors with a large field of view in only one setting.